What option is that? I did a few searches online, including in /usr/src/.config to see if I could find something related to "ZONE" or "TIME", but nothing of interest came up. What do I need in my kernel to make this work? (Yes I have my /etc/localtime linked, to /usr/share/zoneinfo/Europe/Oslo.)

The time data shown in uname is built into the kernel when you compile it. Therefore, if your date command was wrong at the time you built the kernel, your uname output will be wrong indefinitely for that kernel. If this bothers you, build a new kernel now that your date command produces the correct output, and use that kernel instead.